The invention is directed to a joint for cardan shafts, for instance for steering columns of motor vehicles, which shafts have a coupling member configured as a cross pin or a trunnion cross, whose trunnions are rotationally supported in pairs in the end of the two shafts, at least one end of a shaft being configured as a fork.
In this connection, the joint for cardan shafts in the U.S. Pat. No. 2,271,974 must be mentioned. The end of the one shaft is configured to be bell or tulip shaped. A trunnion passing transversely through this joint part and forming a coupling member is supported in this joint part with a widened central portion comprising a central recess, at which central portion bearing bushes with their axes aligned diametrically with respect to each other are shaped or formed on. These bearing bushes are on the external side of the central portion and are offset through 90.degree. with respect to the trunnion axis. The bearing bushes accept a bolt passing through the central recess in the trunnion. The end of the other shaft projects into the central recess of the trunnion, with the shaft having a transverse bore penetrated by the central segment of the bolt. In the bell-like joint part, incisions emanate from its edge at diametrically opposite points, which incisions then widen in a keyhole-like manner. These incisions serve for receiving the trunnion as a coupling member. The width of these incisions corresponds to the diameter of the trunnion serving as a coupling member and the diameter of the adjacent widening corresponds to the external diameter of the housings of the needle roller bearings, which receive the ends of this trunnion. The housings of the needle roller bearings are fixed respectively by means of a lock screw. The coupling member used here is manufactured by machining or metal cutting. This known joint is impractical for a number of reasons, including those discussed below.
The fabrication of the coupling member by machining is too expensive for a mass produced article. Not only the central bore must be produced for receiving the end segments of the one shaft, but also the bores in the bearing bushes for receiving the transverse bolt. The incisions emanating from the edge of the bell-like joint portion, into which the trunnions of the coupling member are pushed during assembly of the joint, weaken this construction part to a considerable extent. Above all, however, the lever arms serving for the force and a moment transmittal for the one end segment of the one shaft protruding into the central recess of the coupling member are as unfavorable as can be imagined when compared to the lever length for the other shaft segment. Forces or moments which can be transmitted by a joint are determined by the load carrying capacity of the weakest link in the joint. Assuming the most unfavorable case for the lever arms on which the computation of the occurring forces and moments are based, namely that the trunnions or the bore carry load only at their outer end, then the length ratio of the two lever arms in this case amounts to approximately 4 to 1.5. Furthermore, it has to be remembered that the bearing carrying the one shaft is arranged on the side of the bell-shaped joint part, so that a not inconsiderable distance exists between the center of the joint and the mentioned shaft bearing, which favors the occurrence of bending loads.
A comparable design is known from the U.S. Pat. No. 1,003,017. Compared to the initially discussed design we are dealing here with an improved solution, since in this case the coupling member is designed as a single piece cross pin or as a single piece trunnion cross. Statements about the type of bearing arrangement in support of the shaft can, however, not be discerned from this publication. This also applies to the cardan shaft in DE-OS 28 18 167, which joint part proper is designed in a similar manner.
A steering shaft is also known from U.S. Pat. No. 4,608,891, which shaft is supported in a shaft tube and whose one end is configured as a fork of a joint, which is not disclosed in greater detail. A ball bearing is provided in the transitional region between the fork and the shaft. A comparable design is also shown in DE-OS 38 11 215. In both cases, the shaft is supported externally of its joint, so that a not inconsiderable distance exists between the center of the joint and the respective shaft bearing, which favors the occurrence of additional bending loads in the joint region, where, in any case high forces already exist for transmitting the torques.